Dancers utilize a 'whip-like effect' to increase arm angular momentum during multiple-revolution pirouette en dehors.

A pirouette en dehors (PeDh) is multiple turns using the angular momentum generated by swinging the arms with both feet on the ground. The purpose of this study was to investigate how the arm swing facilitates increasing peak angular momenta of both arms during multiple PeDh. Upper body movements in single to six-revolutions clockwise (as seen from above) PeDhs were analysed to determine arm's angular momentum induced by the individual joint torque, gravitational force and motion-dependent terms. The horizontal abduction and adduction torques of the right and left shoulder joints, respectively, and clockwise torsional torque of the upper torso induced the clockwise angular momentum (CWAM) of the arms in the horizontal plane, about the vertically upward axis. The motion-dependent term induced the CWAMs after joint torques and contributed to the maximum total CWAM of both arms substantially. The CWAMs induced by the motion-dependent term increased with joint torques up to the triple PeDh in the right arm but independently from the left shoulder joint torque up to the sextuple PeDh in the left arm. Using a whip-like motion of the arm, increasing the arm joint torques would not be required necessarily when performing, i.e., more than quaruple PeDhs.

Optimized Simulation of Upper Body Timing on the Production of Bat-Head Speed in Baseball Batting.

The objectives of this study were to (1) investigate the effect of the timing of the upper body joint motions in baseball batting on the bat-head speed and (2) develop and evaluate a simulation model inputting the individual hand forces on the bat. Twenty-three male collegiate baseball players performed tee batting set at waist height. A 10-segment angle-driven simulation model consisting of a bat and upper body was driven using the coordinate data of the standard motion. Performance optimization was conducted by changing the timing of the joint angle time histories of the upper body to increase the maximum bat-head speed. The optimization simultaneously estimated the individual hand forces by polynomial approximation dependent on the total bat forces to assess joint torques of the upper body. The bat-head speed increased to 39.2 m/s from 35.6 m/s, and the optimized timings were characterized by the earlier timing of the barrel-side elbow supination, wrist radial flexion, torso right lateral flexion, and the later timing of the barrel-side shoulder abduction. It is concluded that the skillful coordination of the individual joint movements for the upper body can produce a higher bat-head speed through effective sequencing of proximal to distal movements.

Kinetics of four limb joints during kick-start motion in competitive swimming.

The kick-start technique in competitive swimming generates a force acting on the starting platform owing to gravity, muscle contraction and resulting joint torque. To understand optimal body movement on the starting platform for maximising take-off velocity, it is necessary to investigate the joint torque in relation to the joint's rotation effects. Joint torques were calculated by inverse dynamics using kinetic and kinematic data. A one-way ANOVA showed significantly greater extensional torque for shoulders than for elbows or wrists, and for hips than for knees or ankles. The results indicated that the force of the hands was mainly influenced by extension torque at the shoulder joint. Hip joint extension torque on the front side lower limb (FSLL) was mainly used for supporting the body weight until hands off. After hands off, the front-foot force originated mainly by increases in ankle joint plantar flexion and knee joint extension torque on the FSLL. Rear side lower limb torque increases in the hip, knee and ankle joints provided the rear-foot force. This investigation clarified the magnitudes and functions of each joint torque acting on the extremities during the kick-start, providing practical information for improving starting performance.

Optimisation of the upper body motion for production of the bat-head speed in baseball batting.

The purposes of this study were to 1) develop a simulation model of baseball batting utilising the standard motion, and 2) explore optimal motions of the upper body to increase the bat-head speed. Twenty-three male collegiate baseball players performed tee batting set at waist height. A ten-segment angle-driven simulation model consisting of a bat and upper body was driven using with the coordinate data of the standard motion. Performance optimisation was conducted to find joint angle time histories of the upper body that increase the maximum bat-head speed. In the evaluation of the simulation model, the root mean square error between the measured and simulation model was 0.19 m/s and 0.98° for the time histories of the bat-head speed and bat orientation angle. Performance optimisation was able to achieve a targeted increase in bat-head speed (35.6 m/s to 40.0 m/s) through greater barrel-side shoulder abduction, knob-side elbow flexion, and torso right lateral flexion around ball impact resulted in the bat accelerating in the hitting direction. It is concluded that the proposed simulation approach can be applied as a tool for further simulation analysis in various complex sporting motions.

Kinetic function of the lower limbs during baseball tee-batting motion at different hitting-point heights.

The aim of this study was to investigate the kinetic functions of the lower limbs at different hitting-point heights to provide key information for improving batting technique in baseball players. Three-dimensional coordinate data were acquired using a motion capture system (250 Hz) and ground reaction forces were measured using three force platforms (1000 Hz) in 22 male collegiate baseball players during tee-batting set at three different hitting-point heights (high, middle, and low). Kinetic data were used to calculate joint torque and mechanical work in the lower limbs by the inverse dynamics approach. The peak angular velocity of the lower trunk about the vertical axis was smaller under the low condition. The joint torques and mechanical works done by both hip adduction/abduction axes were different among the three conditions. These results indicate that hip adduction/abduction torques mainly contribute to a change in the rotational movement of the lower body about the vertical axis when adjusting for different hitting-point heights. In order to adjust for the low hitting-point height which would be difficult compared with other hitting-point heights, batters should focus on rotating the lower trunk slowly by increasing both hip abduction torques.

Direct and indirect effects of joint torque inputs during an induced speed analysis of a swinging motion.

This study proposed a method to quantify direct and indirect effects of the joint torque inputs in the speed-generating mechanism of a swinging motion. Linear and angular accelerations of all segments within a multi-linked system can be expressed as the sum of contributions from a joint torque term, gravitational force term and motion-dependent term (MDT), where the MDT is a nonlinear term consisting of centrifugal force, Coriolis force and gyroscopic effect moment components. Direct effects result from angular accelerations induced by a joint torque at a given instant, whereas indirect effects arise through the MDT induced by joint torques exerted in the past. These two effects were quantified for the kicking-side leg during a rugby place kick. The MDT was the largest contributor to the foot centre of gravity (CG)'s speed at ball contact. Of the factors responsible for generating the MDT, the direct and indirect effects of the hip flexion-extension torque during both the flight phase (from the final kicking foot take-off to support foot contact) and the subsequent support phase (from support foot contact to ball contact) were important contributors to the foot CG's speed at ball contact. The indirect effect of the ankle plantar-dorsal flexion torque and the direct effect of the knee flexion-extension torque during the support phase showed the largest positive and negative contributions to the foot CG's speed at ball contact, respectively. The proposed method allows the identification of which individual joint torque axes are crucial and the timings of joint torque exertion that are used to generate a high speed of the distal point of a multi-linked system.

Modelling error distribution in the ground reaction force during an induced-acceleration analysis of running in rear-foot strikers.

The objective of this study was to develop and evaluate a methodology for quantifying the contributions of modelling error terms, as well as individual joint torque, gravitational force and motion-dependent terms, to the generation of ground reaction force (GRF), whose true value can be measured with high accuracy using a force platform. Dynamic contributions to the GRF were derived from the combination of (1) the equations of motion for the individual segments, (2) the equations for constraint conditions arising from the connection of adjacent segments at joints, and (3) the equations for anatomical constraint axes at certain joints. The contribution of the error term was divided into four components caused by fluctuation of segment lengths, geometric variation in the constraint joint axes, and residual joint force and moment errors. The proposed methodology was applied to the running motion of thirteen rear-foot strikers at a constant speed of 3.3 m/s. Modelling errors arose primarily from fluctuations in support leg segment lengths and rapid movement of the virtual joint between the foot and ground during the first 20% of stance phase. The magnitudes of these error contributions to the vertical and anterior/posterior components of the GRF are presented alongside the non-error contributions, of which the joint torque term was the largest.

A comparison of kinetics in the lower limbs between baseball tee and pitched ball batting.

In this study, the kinetic characteristics of lower limbs during batting were investigated by comparing batting off a tee with batting a pitched ball. Participants were 10 male collegiate baseball players who performed tee batting (TB) and batting using a pitching machine (MB; approximate ball speed: 33.3 m/s). Three-dimensional coordinate data were acquired using a motion capture system, and ground reaction forces were measured using three force platforms. Lower limb joint torques were obtained by inverse dynamics calculations. The results indicated that the angular velocity of the lower trunk was larger in TB than in MB for rotation. The swing time from stride foot contact with the ground to ball impact was significantly longer in MB than in TB. The angular impulses of bilateral hip adduction, pivot hip external rotation, and stride hip and knee extension torques were significantly larger in MB, suggesting that batters exert these joint torques earlier for pitched balls to handle time constraints by changing the rotation of the lower trunk in response to the unknown ball location and speed in MB. These findings will help to fill a gap in the literature and provide coaching insights for improving batting motion.

Kinetic analysis of the lower limbs in baseball tee batting.

The purpose of this study was to investigate effects of the ground reaction forces on the rotation of the body as a whole and on the joint torques of the lower limbs associated with trunk and pelvic rotation in baseball tee batting. A total of 22 male collegiate baseball players participated in this study. Three-dimensional coordinate data were acquired by a motion capture system (250 Hz), and ground reaction forces of both legs were measured with three force platforms (1,000 Hz). Kinetic data were used to calculate the moment about the vertical axis through the body's centre of mass resulting from ground reaction forces, as well as to calculate the torque and mechanical work in the lower limb joints. The lateral/medial ground reaction force generated by both legs resulted in the large whole body moment about its vertical axis. The joint torques of flexion/extension of both hips, adduction of the stride hip and extension of the stride knee produced significantly larger mechanical work than did the other joint torques. To obtain high bat-head speed, the batter should push both legs in the lateral/medial direction by utilising both hips and stride knee torques so as to increase the whole body rotation.